Acaulospora foveata


(reference accession BR861)


Whole Spores

Spore Growth
Red orange to dark red brown spheres with saccules starting to differentiate
Developmental Stages
Red orange to dark red brown spheres
Mature spores


Size distribution slight skew leftCOLOR:  Red-orange (0-50-60-5) to dark red- brown (40-50-70-10). Immature spores initially are cream-colored and gradually acquire an orange tint as the spore wall begins to differentiate (see photo).

SHAPE: Globose to subglobose, sometimes irregular.

SIZE DISTRIBUTION: 240-360 µm (mean = 289 µm, n = 58).

 


Subcellular Structure of Spores

SPORE WALL: Three layers (L1, L2 and L3) are usually evident, with the outer layer continous with the wall of the neck of the parent sporiferous saccule. The inner two layers are synthesized sequentially as the spore forms on the neck of the saccule. A third layer homologous with that in spores of other large ornamented species (e.g., A. tuberculata).

Foveata Spore Structure

L1 and L2 of spore wall with initial depressions in spore wall

Juvenile spore wall with depressions in surface

Side view of spore wall with depressions in surface

L2 of spore wall with depressions L3 of spore wall iw1

Spore wall with depressions in surface

L1: Hyaline, 2-2.4 µm thick; degrading and sloughing with collapse and dehiscence of the sporiferous saccule (see first photo above).

L2: A layer that thickens with synthesis of orange-red sublayers (or laminae); 9-18 µm (mean = 14.6 µm ) thick at maturity. Initially a single layer, 2-4 µm thick, forms in undulations that establish the shape and depth of surface concave depressions (or pits), with additional sublayers forming horizontally beneath to establish a an underlying base (see photos above). Depressions are circular to ovoid, 8-12 µm across and 0.5-3 µm deep in the mature layer. This layer does not produce any reaction in Melzer’s reagent.

L1 and L2 spore wall with depressions

L3: A layer that forms with synthesis of additional concolorous sublayers that are not readily distinguishable in PVLG, but more evident in Melzer’s reagent because it produces a dark red-brown reaction. This layer often is fused with L2, but sometimes separates (see photo above), 3-5 µm thick when measurable. This layer may be homologous with an inner separate laminate layer (L3) in spores of A. koskei and A. laevis.

Spores mounted in PVLG

Iw1 and iw2

Spore wall with depressions and L2 gw2 amorphous

Spores in PVLG & Melzer’s reagent

Spore wall laminate layer iw1 L1 beaded of iw2 L2 of iw2

Spore wall laminate layer iw1 L1 beaded of iw2 L2 of iw2

L1 and L2 of iw1 L1 and L2 of iw2

L2 and L3 of spore wall L1 and L2 of iw1 L2 of iw2

GERMINAL WALLS: Two hyaline flexible inner walls (gw1 and gw2) are present. They can be seen only after spores have completely cleared when mounted in PVLG or Melzer’s reagent, which can take as long as 30 days.

GW1: Consisting of two adherent layers (L1 and L2) are formed, both are of near-equal thickness, ranging from 0.6-1.0 µm thick. This wall forms completely independent of the spore wall and thus has no direct developmental connection with it.

GW2: Consisting of two adherent layers (L1 and L2) are formed that together are 5-12 µm when measured in PVLG. L1 is hyaline, 1.5-2.2 µm thick with granular excresences (or “beads”) that tend to become dislodged and float away when pressure is applied to it. These “beads” are stabilized after preservation in formalin, but otherwise may be absent on mounted spores within a few months of storage. L2 is hyaline and somewhat plastic (probably equivalent to a “coriaceous” wall using traditional terminology). It is 2-10 µm thick in PVLG-based mountants, staining pinkish red (20-80-60-0) to a reddish-purple (40-80-60-0) in Melzer’s reagent.


Cicatrix

A circular to ovoid scar indicating region of contact between spore and saccule neck; it consists of closely packed tubercles surrounding an unornamented depression, 12-16 µm in diameter (mean = 13.8 µm) at its widest.

L2 laminae of spore wall and cicatrix


Sporiferous Saccule

IsotypeINVAM

Saccule and attached spore spore wall and gw1 and gw2

Smashed saccule

COLOR: White to cream when immature, hyaline when emptied of contents.

SHAPE: Mostly globose to subglobose.

SIZE: 260-320 µm, mean = 282 µm

SACCULE WALL: A single hyaline layer with fine sublayers; the outermost sublayers appearing somewhat flakey; 3.5-4 µm thick. In the isotype (see left photo above), flakiness of the saccule surface was more pronounced and the wall was thicker (4-10 µm).

SACCULE NECK: Tapering from the saccule to the region of spore attachment; saccule neck wall hyaline and 1.8-2.2 µm thick

DISTANCE FROM SACCULE TO SPORE: Not measured in spores examined thus far.


Notes

The description of this species (Janos and Trappe, 1982) was based on field-collected spores, many of which appeared to be parasitized by other fungi (see left photo). None of the type specimens contained inner (germinal) walls (see right photo). In fact, the authors only description of such structures is the statement ” .....an adherent but separable hyaline inner layer 3 µm thick”. It is likely, from this measurement, that both gw1 and gw2 were fused together.

The accession from which live spores were obtained is a trap culture and therefore contains more than one species. For that reason, we cannot report mycorrhizal morphology at this time. Attempts to obtain a monospecific culture from extracted spores so far have failed. We continuously maintain the trap culture by reseeding with the expectation of increasing numbers of healthy spores.

Janos and Trappe

Spore Growth

Smashed spore wall with depressions

Red orange to dark red brown spheres with saccules starting to differentiate


High Resolution Images

Red orange to dark red brown shiny spheres mixed with clear saccules
Spores
Spore and saccule begin cream and opaque and end with dark red brown spore and clear saccule
All Spore Stages
Smashed spore in pvlg
In PVLG
Smashed spore in pvlg
In PVLG
Smashed spore in Melzer's reagent dark red orange center
In Melzer's Reagent
Germination orb clear hyphae strings
Germination Orb

Links to Gene Sequences in Genbank

rRNA genes

beta-tubulin gene


Reference

  • Janos, D. P. and J. M. Trappe. 1982. Two new Acaulospora species from tropical America. Mycotaxon 15: 515-522.